Fasteners and Preserved Wood
Wood treatment chemicals can react with metals, so it is important
to use the right type of fastener with treated wood. Recommendations on
fasteners to use with specific types of treated wood have been made by the
treated wood industry, the chemical industry and the connector and fasteners
industries. More testing is under way.
Types of Wood Preserving
Treatments
Chromated copper arsenate, type C (CCA-C) has until
recently been the industry뭩 standard wood preservative, but new treatments have
been introduced. Alkaline copper quat (ACQ) and copper azole (CA) are replacing
CCA-C in products destined for some residential applications. CCA will continue
to be used to treat wood for industrial, commercial and agricultural uses. The
Canadian Institute of Treated
Wood has posted a complete description on its website.
Current
Recommendations on Fasteners for Treated Wood
In general, hot dipped
galvanized or stainless steel fasteners are recommended for use with treated
wood. Aluminum is not recommended. Electroplated galvanized fasteners are also
not recommended.
If hot dipped galvanized fasteners and connectors are to
be used, special attention must be paid to the level of galvanization (there are
different designation). Current recommendations are that heavier galvanization
is required for fasteners and connectors in contact with the new treatments than
was the case for CCA. G60 galvanized fasteners and connectors are used with CCA
treated wood. For ACQ or CA treated wood, use fasteners that meet the ASTM A153
standard. Hot-dipped galvanized connectors to be used with ACQ or CA treated
wood should have a G185 designation as per ASTM A653.
For further
information, please visit Osmose Nature Wood?/a>, Preserve?or
Preserve Plus?/a>, Universal Forest Products ACQ, Wolmanized?Natural
SelectTM.
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Insulation and Ventilation of Wood-Frame Roof
Assemblies
Part 2 - Moisture Control and Climate
Types
Michael Steffen
Moisture control for roof assemblies in all climates should
begin at the 뱒upply?side, using the primary strategies of: 1) interior humidity
control, 2) air leakage control and 3) vapor diffusion control.
Interior humidity control involves mechanical exhaust ventilation
of bathrooms, kitchens, and laundries, dehumidifiers, and whole house
ventilation that includes fresh air intake to dilute moisture levels of the
interior air. Other control measures include installing vapor barriers at
crawlspaces and basements to prevent the introduction of ground moisture, and
terminating ventilation exhaust outlets to the building exterior.
Air
leakage control involves sealing the roof, ceiling, and walls at all
penetrations and perimeters to ensure moist interior air or, in some cases,
moist exterior air, does not leak into the roof assemblies. Minimizing the
amount of leakage is critical to moisture control as air leakage has the
potential to transport much greater quantities of moisture into assemblies than
diffusion. In addition, mechanical pressurization or depressurization of the
building can be used to control the dominant direction of airflow to reduce air
leakage.
Vapor diffusion control generally means installing a
vapor retardant material at the warm side of the insulation. Vapor diffusion
retarders, such as polyethylene sheets, kraft paper-faced batts, and paint
coatings on drywall, have a critical impact on both the wetting and drying
potentials of roof assemblies and must be carefully considered. In many
climates, the vapor drive reverses daily and/or seasonally. Use of materials
that are highly impermeable can lead to problems with interstitial condensation
and mold growth in some climates.
Ventilation drying is really a
second line of defense for moisture control. It is not appropriate in some
climates, nor effective in some roof configurations.
Climate-specific
Strategies
Over the past decade, researchers have undertaken a broad
reassessment of the need for roof ventilation. Many of their findings and
recommendations are found in recent editions of the 밃SHRAE Fundamentals
Handbook?[ASHRAE, 2001]. ASHRAE indicates that the advantages and disadvantages
of roof ventilation be evaluated on a case-by-case basis, with climate the main
consideration. Discussion in the Handbook of Fundamentals is organized by the
three climate zones developed by Lstiburek and Carmody in 1994: heating,
cooling, and mixed.
In heating climates, researchers have emphasized the
need for interior humidity control, airtight ceiling construction, and vapor
diffusion control at the warm [ceiling] side of the construction.
In
mixed and cooling climates, condensation may develop on top of polyethylene
vapor retarders in the ceilings of vented roofs during interior cooling cycles
and lead to mold growth. Current research suggests that roof ventilation should
not be required in cooling climates, and vapor retarders should not be placed in
ceilings, so as to allow drying to the interior.
In mixed climates, roof
ventilation is recommended for back-up protection against moisture build-up in
attics and cathedral ceilings, however, vapor retarders should not be required
at ceilings of vented roofs, again to allow drying to the interior.
Roof Configurations
In addition to climate factors, roof
configuration and insulation type can affect the need for roof ventilation.
Prescriptive code requirements for ventilation have been based on assumptions
about simple roof forms that use low-density insulation materials such as blown
fiberglass, blown cellulose, or fiberglass batts. However, many of
today뭩 roof designs involve complex forms that are difficult, if not impossible,
to ventilate according to codes.
Cathedral ceiling assemblies are often
insulated with rigid foam [extruded polystyrene, expanded polystyrene, or
polyisocyanurate] or spray foam [polyurethane or polyicynene]. The airtightness
and vapor resistance properties of these materials are much different than those
of low-density insulations.
Given these properties, there may be roof
designs, even in heating climates, where ventilation is not required. Again, the
primary moisture control strategies should be incorporated into the design,
along with a high quality of construction. Ventilation may serve as a back-up
strategy where it contributes to the drying potential of the
assembly.
Michael Steffen is a registered architect and Quality
Director at Walsh Construction Company in Portland, Oregon. Part3 of this
article will further discuss principles and details for roof ventilation, and
vapor retarder selection.
A longer version of this article is found in
the Spring 2002 issue, Number 19 of Wood Design & Building. For more
information visit www.woodmags.com, click on the Wood Design & Building
logo, and then MagRack.
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Quick Tip ?Viewing Low-Rise Load Cases
WoodWorks U.S. Shearwalls 2004 generates ASCE 7 low-rise wind
loads. The software calculates load cases for wind acting on any corner of the
building. Once wind loads are generated an arrow will appear on one corner of
the building. This is the corner being considered as windward for the load case
displayed.
You can view other load cases using the Show button. For
example, to change the windward corner, select from the list of Load Directions
in the drop down menu that appears when you click the Show button. For example,
choosing the load direction 밯est to East, South to North?means that the
southwest corner will be shown as windward. Two load cases will be considered
for a southwest windward corner ?winds generally parallel to ridge (i.e. wind
acting primarily on the south face) and wind acting generally perpendicular to
the ridge (i.e. wind acting primarily on the west face). To view either of these
load cases, select from the Wind Direction options in the pull-down menu.
To view the case in which wind acts primarily on the south face, choose a
North-South wind direction. For wind acting primarily on the west face,
choose East-West.
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| Did you know? Building the average house generates 3 to
5 lbs of construction waste per square foot. Depending on location and disposal
fees, builders routinely spend $250 to $1000 per house to haul waste away. Given
that 60% to 80% of all tha waste is recyclable, even a little effort can result
in significant improvement to the bottom line. For tips on how to eliminate
construction waste, please visit Be
Constructive. Source: Wood Promotion
Network | | 
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QuattroTMTimber Engineered Wood Products
Developed at Synergy Pacific뭩 100,000 square foot wood processing
and laminating facility in Armstrong British Columbia, the
QuattroTMTimber product line is the newest evolution of engineered
wood products. This range of kiln-dried, appearance grade, high strength
products provide an alternative to solid wood products. The patented building
block profile used for the QuattroPost and QuattroHeader uses a finger-jointed
perimeter construction with a heart-free center, similar to the high strength
structural tubing used in the steel industry.
Manufacturing
Prior to manufacturing, lumber is kiln-dried and
tested for moisture content to ensure that adhesive and stability standards are
met. The raw material is then merchandized and graded to eliminate defects and
ensure product consistency. The finger-jointing process combines structural
adhesives with a 9/8th inch long structural finger. The products are processed
through molders where the profile is applied within four thousandths of an inch
precision. The molded pieces of lumber are then assembled into the individual
Quattro-configurations utilizing either a phenol-resorcinol adhesive or an ASTM
2559 tested clear polyurethane adhesive. The glued-up pieces are then pressed
together in one of two specially designed presses depending on the product and
size.
Products
The QuattroPost is an engineered structural
porch post and column available in SPF, Doug-Fir, and WRC able to withstand
allowable axial loads (0.167 eccentricity) between 12390 to 14629 lbs, for a
nominal 8-foot long 6x6 D.Fir product. It is available in sizes from 4x4 to 8x8
and in lengths 6?to 20?depending on size. Non-load bearing columns may be any
size and length produced. The QuattroHeader will be available in SPF or Doug-Fir
species in sizes from 4x6 to 4x12, and lengths from 8?to 20? The structural
attributes of the QuattroHeader vary with species and construction methodology,
however the expected range of the Modulus of Elasticity is 1.4 to 1.8 million
psi.
Advantages
?A lightweight design facilitating handling,
shipping and installation while enhancing the appearance and structural
performance of solid wood;
?Ensures that moisture in the wood only has to
move a short distance to equalize with local conditions which assures that the
product will not split, twist, or contort;
?Factory controls ensure product
quality and virtually eliminate waste;
?Thirty to forty percent improvement
in fiber utilization on small logs improves environmental appeal;
?High
strength, compression and reliability ratings;
?Hollow center design allows
for reduced weight and the void accommodates running electrical wires or
irrigation lines;
?Varieties of finishes reduce on-site labour and finishing
costs.
Handling and Installation
On the building site,
QuattroTMTimber should be kept in covered storage off the ground on
spacers every 6 feet. All lifts should be covered by plastic shipping wrap
opened around the bottom to permit free airflow. For primed products, any end
cuts should be primed before nailing using an alkyd-oil primer or equivalent.
For posts, a mounted bracket should be used on the bottom to allow ventilation
and prevent water damage. To prevent splitting, pre-drilling is recommended for
fasteners. Quattro products exposed to weathering should be given the same
durability considerations as other natural wood fiber
products.
Quality and Certification
Synergy Pacific has been
issued the certificate of compliance with the requirements of the international
standards governing structural glue laminated timber by CanPly, an
internationally recognized certification and testing authority. Synergy Pacific
has also successfully tested the performance of its finger-jointed products
against the National Lumber Grades Authority (NLGA) Special Products Standards
(SPS) for Finger-Jointed Lumber, and is currently completing the formal
certification process with the ICC for use in the US. This final approval is
expected in February 2004, CCMC certification in Canada will follow shortly
thereafter.
For further information on the complete line of
QuattroTMTimber products including literature, physical properties,
testing, samples, or pricing, please call Synergy Pacific at (250) 546-6808, or
contact them by email. You can also visit their website at www.synergypacific.com.
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CWC's US Span Books a Big Hit at the 2004 Builders Show!
The 2004 National Association of Home Builders (NAHB) International
Builders?Show (IBS) in Las Vegas, Nevada held from January 19th to the 22nd saw
a record-breaking attendance of 104,627 visitors. The Canadian Wood Council
(CWC) exhibited its distinct 900 square-foot booth fully constructed using wood
materials and distributed over 3,300 US Span Books and 9,000 other CWC
publications to building professionals.
Both CWC staff and Members
(including Structural Board
Association, CANPLY, Abitibi-Consolidated, Tembec, Structurlam, Weldwood, and industry partner representatives from FPAC) were also there to offer
information directly to the building community. Again this year, CWC
participated in WPN뭩
Show promotion, which consisted of a truck giveaway ?and a chance to win $1
million dollars. Most frequently asked questions and concerns included the price
fluctuations of OSB and Plywood in 2003, and the slowing US economy and need for
a more skilled US labour force. For the full story please visit CWC
Events. For more information about NAHB뭩 IBS visit www.buildersshow.com.
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Wood Solutions Fair
 Westin Bayshore Resort & Marina
March 10, 2004
Vancouver,
BC
For more information visit www.woodsolutionsfair.com
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48th Annual CSI Show & Convention
 McCormick Place
April 21-23, 2004
Chicago, IL
For more
information visit www.thecsishow.com
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Wood Solutions Fair
Washington State Convention Center
April 22, 2004
Seattle,
WA
For more information visit www.woodsolutionsfair.com
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48th Annual CSI Show & Convention
McCormick
Place
Booth 1192
June 10-12, 2004
Chicago, IL
For more
information visit www.aia.org | | |
